Hazardous and Radioactive Waste Treatment Technologies Handbook - Chapter 4 pps

© 2001 by CRC Press LLC Chapter Four Thermal Treatment Technologies © 2001 by CRC Press LLC 4.1 Incineration Systems John N. McFee and Charles Pfrommer, Jr. IT Corporation, Knoxville, Tennessee Michael L. Aident IT Corporation, Englewood, Colorado Introduction Incineration has been used by industry since the 1930s to deal with troublesome wastes (Cudahy, 1999). At that time, it was developed as a permanent solution for organic industrial wastes that could not be discharged into streams and waterways without noticeable results. With that start, incineration became a process option for industrial wastes, municipal wastes, environmental restoration clean-ups, radioactive wastes, medical wastes, and virtually any organic material that represents an environmental hazard. This chapter section describes several conventional incinerator types, with emphasis on the special issues related to the treatment of radioactive and mixed wastes. Radioactive waste incineration has been practiced since the 1950s for volume reduction and con- version of slightly contaminated fibrous waste to forms amenable to immobilization (Perkins, 1976). The earliest radioactive waste incinerators were variations on the fixed hearth or controlled air incin- erators. These were manual feed/manual discharge systems. In the 1980s, several manufacturers offered radioactive treatment systems based on common incinerator designs for the treatment of wastes from nuclear power stations. With the definition and regulation of mixed waste, the focus has turned to demonstration that these same incinerator designs acceptably address the hazardous and toxic con- stituents of radioactive waste. In general practice, incineration is the high-temperature oxidation of a waste material for the purpose of volume reduction, energy recovery, or detoxification. The U.S. Environmental Protection Agency (U.S. EPA) provides a definition in 40 CFR 260.10: a closed device that uses controlled flame combustion  This definition has supported the exclusion of some non-flame oxidation systems from the hazardous waste incineration regulations. Two general introductory topics are briefly covered in this section: the chemistry of incineration and design considerations. These topics support the subsequent specific incinerator discussions by providing general background for the evaluation and selection of specific units for specific applications. The chemistry of incineration topic presents waste oxidation chemistry as the energy content of the materials and the oxidation mechanisms have substantial impact on the selection of a specific incinerator for a task. The second topic, design considerations, details how physical properties of waste affect selection and design of an incinerator. One of those design aspects is organic destruction efficiency, which is commonly advertised as a performance criteria for an incinerator type. However, it must be recognized that this critical incin- erator performance parameter is not solely a function of the primary incineration component. It is controlled by the design and operation of the complete incinerator system; the primary combustion system: the secondary combustion chamber or afterburner, and off-gas treatment system. The U.S. EPA surveyed the performance data from 162 incineration systems in development of the 1999 Com- bustion Rule. These 162 units all met the applicable destruction and removal efficiency requirements © 2001 by CRC Press LLC of the Resource Conservation and Recovery Act, at least 99.99% for the tested organic constituents (U.S. EPA, 1995). Therefore, it can be stated that essentially all incinerator types that are designed and operated properly are capable of providing compliant destruction of organic compounds. Chemistry of Incineration Basic Combustion Equations Incineration is defined in general terms as the controlled combustion of organic matter. All organic matter is composed of various elements, including carbon (C), hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), Chlorine (Cl), and other elements. The concentration of each of these elements in the organic matter determines the specific organic compound and its chemical and physical properties that will impact the selection and sizing of an incineration system. Most analyses of incineration systems can be accomplished based on the laws of thermochemistry and thermodynamics. The reaction mechanisms that occur and the intermediate compounds that form during the combustion process can be very complex. However, the combustion analysis depends predominantly on the initial reactants and the final products of the combustion reactions, and not on the actual path taken to reach the final products. For example, the combustion mechanism for propane (C 3 H 8 ) may be as follows. The propane is first thermally cracked to methane (CH 4 ) and ethylene (C 2 H 6 ). From these intermediate compounds, the oxidation begins and may first oxidize the organic molecules to carbon monoxide (CO) and subsequently completing the oxidation by converting the CO to carbon dioxide (CO 2 ). The fact that there were several intermediary products between the propane (C 3 H 8 ) and the CO 2 is generally not significant in the overall analysis of the system thermochemistry. With this said, environmental regulators have turned their attention from looking at the destruction efficiency of the incinerator to the concentration of the products of incomplete combustion (PICs) from the incinerator and their associated risks to the public. PICs are intermediary organic species and those formed by side reactions in the combustion system. The regulation of PICs from an incinerator plays a significant role in the design of the combustion process to ensure essentially complete destruction of all organic species to form CO 2 and water. In some systems, additional control technologies are added to the gas cleaning system to control PIC emissions to the regulated levels. The simplest way to evaluate combustion in an incineration system is on a molecular level. As such, one or more of the following generalized reactions may represent the basic combustion reactions: C + O 2 = CO 2 (4.1.1) C 3 H 8 + 5O 2 = 3CO 2 + 4H 2 O (plus trace CO emissions) (4.1.2) H 2 O(l) = H 2 O(g) (liquid to gas phase change) (4.1.3) 2C 6 H 5 NH 2 + 15 1 / 2 O 2 = 12CO 2 + 7H 2 O + N 2 (plus trace NO and NO 2 emissions) (4.1.4) C 6 H 5 Cl + 7O 2 = 6CO 2 + 2H 2 O + HCl (example of chlorinated organic) (4.1.5) Cl 2 + H 2 O = 2HCl + 1 / 2 O 2 (equilibrium reaction) (4.1.6) S + O 2 = SO 2 (plus trace SO 3 emissions) (4.1.7) Note that these reactions show sufficient oxygen to complete the oxidation of C to CO 2 . If there is insufficient air or oxygen present, only partial oxidation (e.g., C to CO, etc.) will take place. As discussed previously, partial oxidation can result in higher levels of PICs. However, a number of systems are designed to meet the emissions standards operating in the pyrolytic mode in the primary combustion chamber and completing the oxidation in the secondary combustion chamber. © 2001 by CRC Press LLC The carbon component of organic waste can be either as a volatile or fixed carbon. The volatile portion of the organic is vaporized in the combustor at temperatures less than 800°C. For example, turpentine represents the condensed volatiles from the destructive distillation of wood. The volatiles are combusted either immediately, as is the case with an oxidative combustion chamber, or are carried away with the flue gas into a secondary combustion chamber (SCC) for oxidation in the gas phase. The fixed carbon is the non-ash residue that remains in the waste after the volatiles have been driven off. Typically, the fixed carbon consists almost entirely of combustible carbon. Coke and charcoal are typically encountered forms of fixed carbon. The fixed carbon is more difficult to oxidize and can be the limiting design parameter for solid residence time in solid waste incineration. The amount of fixed carbon in waste can be an issue in the selection and design of an incineration system. For example, when processing wastes in a fixed hearth furnace, very little of the fixed carbon is typically oxidized. This could result in an ash material with a high loss on ignition (LOI) measurement, and analysis of residual combustible material in the ash. In some applications, the LOI of the ash residue from the combustor is a design and performance requirement mandated either by the client or a government regulatory agency. High residual carbon in the ash may be detrimental if ash immobilization is planned, as is the case for most mixed waste applications. Many of the immobilization agents are sensitive to carbon content. Inert matter, also referred to as ash, in the waste feed to the combustor essentially passes through the combustion process either unchanged or is converted to solid oxides or salts. Depending on the physical form of the waste, the ash can be exhausted from the combustor as particulate matter (called particulates or fly-ash) in the flue gas or discharged from the combustion chamber as bottom-ash. The quantity and physical form can have substantial impact on system selection, as some systems can process noncom- bustible items such as metal parts, whereas other systems would simply accumulate these items until shutdown. Ash constituents also significantly impact the design of the incineration system. For example, wastes containing sodium, potassium, and silicon in the necessary proportions could soften, melt, and agglomerate in systems when the ash is raised to high temperatures. If the selected system is a slagging unit or a melter design, then the melted ash is easily processed. Ash softening in non-slagging systems can lead to process plugging and eventual shutdown for removal. The flue gas from a combustion system designed to process solids and sludges will typically contain particulates. These particulates will be ash or unburned organic material that is entrained in the flue gas. Depending on the type of combustion system, the entrainment of the ash in the flue gas could be 5 to 20% of the ash in the waste feed. Particulates in the flue gas will also result from the combustion of liquid wastes in a burner or the atomization of liquids in the combustor. Almost all of the inert material in the liquid wastes atomized in a combustion system will result in particulates in the flue gas. The particulates from the atomization of liquid wastes in a burner are typically the most difficult to treat and remove in the downstream gas cleaning system because of their tendency to form submicron-sized particulates. Because of the high flame temperatures in liquid waste burners, these particulates may be in a melted form, which also challenges system design. Trace Emissions The combustion of waste materials will almost always result in a flue gas that contains low concentrations of various pollutants. Many of these trace emissions are regulated and therefore must be controlled. The primary control method is to minimize the initial formation of the pollutant with specific designs of the combustion system. Gas cleaning technologies are then added downstream of the combustion process to remove the remaining pollutants before the flue gas is exhausted to the atmosphere. Some of the more frequently encountered trace emissions include HCl, SO 2 , NO x , CO, particulates, metals, and PICs. Trace emissions can be the result of a number of factors, including the combustion technology selected, the design of the combustion system, the presence of pollutant progenitors in the feed, and the system operating conditions. Carbon monoxide, for example, is typically formed in the combustor due to low combustion temperatures, poor mixing, insufficient excess air, or very short residence times. The trace © 2001 by CRC Press LLC emissions can also be formed in the downstream equipment, such as in an energy recovery boiler. Off- gas treatment systems and boilers that provide long residence times within a certain temperature range can promote the formation of various trace emissions such as polychlorinated dibenzo-dioxins (PCDD) and polychlorinated dibenzo-furans (PCDF). Much work has been done to study the formation mech- anism of dioxins from combustion systems. Data has shown a direct relationship between the residence time of the gases at intermediate temperatures after the combustion chambers and the concentration of dioxins in the flue gas. (Acharya, 1999). Typical Combustion Gas Composition The typical composition range of the gases from the combustion of waste in an incinerator is illustrated in Table 4.1.1. The compositions shown in this table are for the gas leaving the combustion system and entering the downstream off-gas cleaning system. It should be noted that the flue gas composition is directly related to the waste feed materials and operating conditions of the incinerator. Design Considerations Incinerator selection is actually the specification of a complex array of interrelated components, of which the primary combustion chamber is only one part. A complete incineration system is typically composed of the following components: 1. Waste receipt system to confirm compliance with the waste acceptance limits and capabilities 2. Waste feed storage and preparation (tanks for storing and blending liquid wastes; pits or storage buildings for solid wastes; shredders and other size reduction operations for solid wastes; tanks and special pumps for processing sludges and thick liquid wastes; etc.) 3. Primary combustion chamber selected to address the waste type, quantity, and composition (rotary kiln, fixed hearth, etc.) 4. Secondary combustion chamber or afterburner to complete oxidation of gases and comply with emission requirements for unburned hydrocarbons (the secondary combustion chamber can also be used for liquid waste incineration) 5. Ash removal system to remove ash and non-combustibles from the primary chamber, and cool it for subsequent handling and treatment 6. Ash and non-combustibles treatment system for immobilization or other treatment required to meet disposal site requirements 7. Gas cleaning system to control particulate, acid gas, and other emissions 8. Energy recovery (e.g., steam generation) and plume suppression may also be included in the design of an incineration system 9. Utility systems providing power, water, and process consumables TABLE 4. 1.1 Typical Secondary Combustion Chamber Off-gas Composition and Conditions Off-gas Constituent Range Nitrogen (N 2 ) 6085% Water vapor (H 2 O) 630% Carbon dioxide (CO 2 ) 515% Oxygen (O 2 ) 314% Acid gas (HCl) 0100,000 ppm v Acid gas (SO 2 /SO 3 ) 0100,000 ppm v Nitrogen oxides (NO x ) 15300 ppm v Carbon monoxide (CO) 0100 ppm v Particulates 2024,000 mg/dscm Note: All values in above table except water vapor are on a dry gas basis. © 2001 by CRC Press LLC In the primary and secondary combustion systems, complete oxidation of waste is achieved by close attention to the 3 Ts of incineration design: Time, Temperature, and Turbulence. Sufficient air or oxygen must be intimately mixed (turbulence) with the organic material to complete the oxidation, with sufficient reaction time (time) available to complete the oxidation reaction. As discussed, this time factor is relevant to both the incineration of volatiles in the gas phase and the fixed carbon remaining in the solid phase. As for temperature, the oxidation reaction is generally faster at higher temperatures, but higher temperatures can lead to melting of noncombustibles and residuals. Designers must also focus on providing adequate turbulence in solids combustion systems as that has been found to be a more difficult design factor than time and temperature on the destruction of volatile organics in an incinerator (Lee, 1988). Impact of Waste Types A key aspect to the selection and operation of an incineration system is the nature of the wastes and how they can be prepared and fed to the combustion system. In general, designers strive to provide the incinerator a waste feed that is uniform in size, composition, and feed rate. This leads to controlled, steady operation and high oxidation efficiencies. In the subsequent discussions of specific incinerators, the particular waste types appropriate for each incinerator design are indicated. Gaseous Waste Vapors from process vents and other such sources can be treated by incineration. Technologies other than incineration for handling this type of waste stream include adsorption on activated carbon, chemical absorption in packed towers, UV photolysis, and flameless thermal oxidation. Liquid Wastes Liquids are normally atomized or sprayed into a high-temperature combustion chamber for complete oxidation. If the liquids have sufficient heat content, 3 × 10 6 to 4.5 × 10 6 cal/kg (5000 to 8000 Btu/lb.), they are fed through a burner and can supply the heat or ignition source to support incineration of other less energetic wastes such as aqueous liquids or sludges. These high-energy liquid wastes can be fired in either a primary or a secondary combustion chamber, depending on the energy requirements in those subsystems. Alternatively, waste solvents or oils with higher heating values can be mixed with other low- energy wastes to provide a blend appropriate for good combustion. The viscosity of wastes fired through a burner must be low enough for proper atomization in the burner. Liquids with viscosities below 750 SSU (165 centistokes) can be atomized, but proper atomization can only be achieved by many burners when the liquid viscosities are below 100 SSU. Blending of the wastes is frequently used to meet the viscosity requirement. Nozzle openings for burners are small, so strainers are necessary in most waste liquid systems to prevent plugging. Nozzle selection is specific to the liquid properties to ensure proper atomization and combustion. Aqueous Wastes Aqueous wastes and other liquids with low heat values are frequently atomized through slave or secondary atomizers located near the primary burner or other heat sources where the aqueous waste is evaporated and organic contents oxidized. Aqueous wastes are sometimes used to provide a heat sink, a way to help control the temperature within the combustion system when high-energy wastes are being burned. Solid Wastes Solid wastes can be fed to incinerators in large packages or shredded and metered into the primary chamber. The mechanical reliability of the solids feed system can become a process-limiting parameter for incineration system operation and particularly important for mixed waste systems. Therefore, much effort is spent on evaluating and designing the receiving, storage, preparation, and feeding of solid wastes. Solids can be received in bulk, boxes, drums, and other containers of varying sizes. The preparation (size reduction, mixing, and blending) of these solids is critical for successful system operation. For many incineration systems, it is advantageous, and frequently necessary, that large solids be size reduced by shredding in order to be fed to the system and properly combusted. Smaller sized solids are © 2001 by CRC Press LLC more easily oxidized than larger materials. Containers, such as drums, are generally emptied and/or shredded before being fed. Large rotary kilns and fixed hearth incinerators can be designed to accept drums and large packages. However, design and feed composition limits must be imposed on these packages to avoid overpressures in the system or the release of incompletely oxidized organics. To address the issue of feeding solid wastes of varying composition and energy contents, most appli- cations require waste screening and blending. Because of differing energy and volatiles contents, solid wastes may also need some level of blending. For example, a sudden change in the feed from a slow burning, low heat value wet waste to a rapid burning, high heat value plastic waste could challenge control systems to maintain proper incineration conditions and subsequently impact the gas cleaning system performance. Sludges The term sludge can refer to any waste that is viscous or that contains too much solid to be considered a liquid waste, yet which is too fluid or sticky to be handled as a solid waste. Sludges are stored in tanks, pits or drums and are fed to the incinerator using special equipment (pumps, extruders, or conveyors) designed to handle dense materials containing relatively large solid particles. Blending with other liquid wastes to modify handling properties is also a common production process. These wastes may have high or low heating values. One design challenge for sludge incineration is proper atomization or dispersion in the incinerator to ensure good drying and combustion. Combustion Efficiency As discussed, one object of incineration is to volatilize and oxidize the organic constituents in the waste. Volatilization is enhanced by the atomization of liquids and by the high temperatures achieved by the burning process. The remaining fixed carbon oxidation is a much slower process than the gas-phase oxidation of the volatiles. An element of incinerator design is proper primary chamber operating tem- perature, residence times, and sufficient air/waste contact to support combustion of the fixed carbon. Complete oxidation of volatile organic components is not always achieved in the primary combustion chamber, especially in rotary kiln systems where combustion air is seldom introduced into the system in such a manner as to pass through the bed of waste material. For this reason, afterburners or secondary combustion chambers (SCCs) are used in many incineration systems to complete the oxidation of the organic materials that were vaporized and/or partially oxidized in the primary combustion chamber. A well-designed SCC achieves good turbulence by mixing the primary chamber off-gases with addi- tional combustion air to complete the oxidation process. The temperature in the SCC is frequently higher than the temperature achieved in the primary chamber because the temperature in the primary chamber is controlled to minimize melting or slagging of the solids and ash residues. Slag can plug air inlets, form dams that hold back solids, chemically attack the refractory, and create other problems in the combustion system. An exception to this design practice is for those incineration systems that are designed to operate at high temperatures in the slagging mode to melt and glassify the ash that is discharged. Although laboratory data indicates that complete volatile organic oxidation can be achieved in less than a second under good mixing conditions with a high enough temperature, many incineration systems are designed to provide a minimum of a 2-second retention time of the gases in the SCC (based on off-gas conditions). The design of the SCC is primarily based on achieving good mixing of combustion air with the primary off-gases. The SCC can be upfired, a vertical system in which the primary off-gases enter at the bottom and SCC off-gases exit at the top. Downfired and horizontal SCCs are also used. Slagging can also occur in the SCC because of solids entrainment from the primary off-gases and ash melting (from ash constituents in the liquid wastes being fired). Vertical SCCs are typically used in these applications to allow the slag to flow down and out of the SCC. Where slag can flow out, the bottom of the SCC must be designed for the removal of this material. Controlled Air Combustion The quantity of air introduced into a combustion chamber is controlled. The dual function of air in the incinerator is to provide both oxygen for combustion and cooling/temperature control for high-energy © 2001 by CRC Press LLC wastes. Too much air will lower the combustion temperature and reduce combustion efficiency. Too little air can result in higher temperatures than desirable for the combustion chamber or insufficient oxygen to complete the oxidation of the waste materials. A combustion system that is operated controlled-air is sometimes referred to as a pyrolytic, starved air, or substoichiometric operation. A primary combustion chamber that is operated with excess air is typically referred to as oxidative operation. In all cases when controlled air combustion is used, there is at least one additional oxidation stage (secondary combustion chamber) to complete the oxidation of the organics, carbon monoxide, and hydrogen. Controlled air combustion has been used in the incineration industry to optimize the combustion process for the treatment of solid and sludge wastes and also to control NO x emissions. The combustion air and operating temperatures are controlled in the primary combustion chamber to dry wastes and drive off volatiles at a controlled rate. As the name implies, it is important in a controlled air combustion system to limit the amount of air that is allowed to enter the primary combustion chamber and react with the organics. There are several benefits to operating with controlled air combustion, including: 1. The dual temperature regimes between the primary and secondary chambers facilitate good organic destruction at the high-temperature secondary chamber while avoiding melting of ash and non-combustibles in the lower-temperature primary chamber. 2. Energy released from the partial combustion and volatilization of the waste in the first stage combustor is less than if the wastes were completely incinerated. 3. The volume of flue gas exiting the first stage combustor is reduced because the amount of combustion air is less than that required for complete oxidation of the organics. 4. Flue gas from the first stage combustor will include partially oxidized compounds such as carbon monoxide and hydrogen gas that provide significant energy to increase the temperature of the flue gas up to the operating temperature of the SCC. 5. The volume of flue gas exiting the SCC in a controlled air combustion system can be significantly less than the flue gas from a similarly designed oxidative system. The amount of reduction depends on the quantity of volatile organics in the waste. The more volatiles in the waste, the greater the reduction in flue gas volume. This is because in the controlled air combustion system, many of the volatiles in the solid and sludge wastes are not burned until they reach the SCC, where they are oxidized and the energy is released. 6. Flue gas exiting the primary combustion chamber contains very little oxygen. Typically, at tem- peratures above 650°C, any oxygen that enters the flue gas will react immediately with volatile organics. With the amount of oxygen controlled in the primary and secondary combustion chambers, side reactions are greatly reduced. For example, controlled air combustion is used to limit the formation of NO x emissions in combustion processes. Control of combustion air is also a significant design parameter for mixed wastes containing toxic metals. Common mixed waste contaminants include toxic heavy metals such as arsenic, mercury, lead, and chromium. If an incinerator is operated at high temperatures, the quantity of heavy metal vaporized from the ash and leaving the combustor in the exhaust gas tends to be higher relative to a system operating at a lower temperature. These metal emissions must then be removed by additional components in the gas cleaning system. Essentially, all incineration systems are operated under a slight negative pressure so that air leaks into the system rather than having partially oxidized vapors and particulates leaking out. This is especially important for mixed waste incinerators where the particulate matter may be radioactive. Therefore, control of air infiltration must also be considered in the design of waste feed and ash removal systems. Incinerator Sizing Incineration systems are sized primarily according to the amount of heat released in the combustion chambers. Approximately one cubic meter (1 m 3 ) of combustion air is required for each 890 kilocalories (kcal) of heat released by the burning of waste and auxiliary fuels (North American, 1965). Thus, a © 2001 by CRC Press LLC specific volume of combustion off-gas is generated for a specific quantity of heat released, with relatively small variations caused by water evaporation and other constituents. The gas cleaning system and other downstream unit operations are sized according to the volume of off-gas generated, and are therefore sized in relation to the amount of heat released. The turndown capability of an incinerator to operate at less than the design feed/energy input rate is an important design and system selection consideration. An incinerator operates most efficiently near its design conditions. Some incineration systems can be operated at about 50% of their design, depending on the type of incinerator. The requirement to run at less than design capacity may be costly from an energy perspective. Most incineration systems are designed to operate 24 hr a day, rather than being operated for only a portion of a day or week. This avoids the time loss for programmed heat-up and cool-down of the refractory lining. Conventional Mixed Waste Incineration Systems The following subsections present general design concepts on a few specific conventional incinerator types with a focus on those used for mixed waste incineration. The principal design differences between conventional and radioactive/mixed waste incineration systems are in two areas. The combustion cham- bers must be of designs that preclude fugitive emission of radioactive particulate matter. For this reason, many of the simpler incineration designs for municipal waste have not found favor in the radioac- tive/mixed waste arena. A second feature that drives system selection is the need for a low carbon residual ash. The ash from a radioactive waste processing system is generally immobilized prior to disposal. Many solidification agents are sensitive to residual carbon, so the incinerators themselves must provide a low carbon ash. Table 4.1.2 provides a brief introduction to the applications and issues of the selected incinerator types. Liquid Injection Incinerators A liquid injection incineration system is generally the simplest of combustion systems, as it can be a single burner mounted in a refractory combustion chamber (Aident, 1998). Liquid wastes are also fired in the primary and secondary combustion chambers of other incineration systems. A liquid incineration system is typically used when other waste treatment or disposal options are unavailable or when the liquid wastes may be problematic for other treatment systems. Liquid wastes with relatively high con- centrations of halogens or ash, for example, may not be acceptable for boilers or cement kilns. Figure 4.1.1 is a schematic of a typical liquid injection incinerator. Because of the high temperature of a burner flame, the ash (metals, salts, etc.) constituents in the liquid wastes can vaporize as the liquid is burned. The ash vaporization, however, depends on the ash elemental composition. The condensing of these vapors will result in submicron particulate that must be considered in the selection and design of a gas cleaning system. Alternatively, the ash in the waste liquid could melt and form sticky particulate that could adhere to the walls of the combustion system TABLE 4.1.2 Mixed Waste Incinerator Types and Applications Incinerator Type Waste Types Accepted Applications Liquid injection Liquids Small or large industrial Fixed hearth Packaged solids in primary chamber and liquids in secondary chamber Used for small packaged mixed waste applications Rotary kiln Liquids, sludges, solids Used on large mixed waste applications with multiple waste types Fluidized bed Liquids, sludges, shredded solids Specialized applications in High Level Wastes Multiple hearth Sludges, solids Potential waste applications identified Car-bottom furnace Large metallic solids Potential waste applications identified © 2001 by CRC Press LLC or on the walls and other components of the gas cleaning system. The ash can also form eutectic mixtures that attack, weaken, and ultimately destroy the incinerator refractory. Larger liquid incineration systems frequently have multiple burners. At least one of the burners will be fired with good fuel value liquids, but the other burner(s) may be firing wastes that will not indepen- dently support a flame. The primary burner may be fired with auxiliary fuel. The secondary burners, sometimes called slave burners, may be processing aqueous wastes or poor-quality burner fuels. The atomization of these wastes in the combustion chamber enhances the evaporation of the water component and provides for destruction of the organic species. Unlike most other incineration systems, liquid incineration systems can be designed to operate under pressure. One type of liquid incineration system is a down-fired unit where the burner is mounted on top of a vertical combustion chamber and the bottom of the chamber is submerged several inches in a water sump. As the combustion off-gases pass through the water in the sump, they are quenched to their adiabatic saturation temperature. The gases then pass into the gas cleaning system. It is not unusual in this type of system for the combustion air blower and combustion chamber to operate at pressures as high as 1.3 atmospheres, thereby providing the motive force for flow through the gas cleaning system and eliminating the need for an induced-draft fan. Table 4.1.3 lists the advantages and disadvantages of liquid injection incinerators. Fixed Hearth (Controlled Air) Incinerators In the development of incinerators, the simple fixed hearth has occupied a continuing role for small applications, including mixed waste. One of the simplest fixed hearth incinerators is a rectangular, refractory-lined chamber (firebox) where a door is opened and waste is manually placed onto the floor of the firebox. The door is closed and a burner is turned on to heat up the firebox to temperatures in the range of 1000°C (1800°F). With the firebox at temperature, air is injected into the firebox from the FIGURE 4.1.1 Liquid injection incinerator schematic. COMBUSTION AIR A QUEOUS WASTE INJECTOR DISCHARGE TO POLLUTION CONTROL SYSTEM LIQUID BURNER LIQUID WASTE FUEL INJECTOR [...]... Incineration and Thermal Treatment Technologies Conference, Orlando, FL, May © 2001 by CRC Press LLC Dempsey, C.R., and E.T Oppelt, 1993, Incineration of hazardous waste: a critical review update, J Air & Waste Mgmnt., 43 , 25–73 Freeman, H.M., Ed., 1988, Standard Handbook of Hazardous Waste Treatment and Disposal, McGrawHill, New York Huhyh, Vu X., and C.A Parker, 1996, Evaluation of a transportable hot-gas... all organics and fixed carbon in the waste This system was designed in Denmark by Studsvik and is now being used by GTS Duratek in Oak Ridge, Tennessee to treat low-level radioactive contaminated waste The advantages and disadvantages of fixed hearth incinerators are listed in Table 4. 1 .4 TABLE 4. 1 .4 Fixed Hearth Incinerator: Advantages and Disadvantages Advantages Accepts packaged waste and still provides... widely used in wastewater plant sludge incineration and have been used in specific hazardous waste applications Energy recovery from the hot off-gases is common as well, including in-bed heat transfer tubes to recover energy and reduce excess oxygen during incineration of high-energy wastes The advantages and disadvantages of fluidized bed incinerators are summarized in Table 4. 1.6 TABLE 4. 1.6 Fluidized... evidenced by the fact that man-made and natural glasses have survived in the environment for thousands to millions of years, respectively; (2) glasses can be made over wide ranges of composition and can therefore tolerate correspondingly wide variations in waste composition; and (3) the basic glass-making process is relatively simple and robust, making it well-suited to hazardous and radioactive production... the impetus for interest in vitrification as a potential treatment technology for numerous other waste management problems, including other types of radioactive wastes as well as hazardous wastes The process of vitrification is attractive because it can destroy hazardous organics present in the waste and chemically incorporate the radioactive and hazardous inorganic constituents into a stable glass product... preparation/pretreatment; glass melter; off-gas system; and product handling Feed Preparation/Pretreatment This may include some or all of the following: waste feed handling, size reduction, drying, calcining, blending with glass forming chemicals (GFCs) and other feed additives, and transport to the glass melter More extensive pretreatment steps can also be included, such as the removal of troublesome waste. .. fiber, and tiles In radioactive systems, the product handling system would also include closure and decontamination of the product container Operation and integration of these four main areas of the vitrification systems also involve process control systems, instrumentation and monitoring, and a variety of support systems and services, including the power supply and control systems and services and utilities... with radioactive wastes, for which the glass product is still radioactive and must be disposed accordingly, vitrification can render hazardous wastes non -hazardous, which opens up the additional possibility of product reuse; typical uses of the product include aggregate, abrasives, coatings, fibers, insulation, and tiles Clearly, such beneficial reuse offers the possibility of offsetting some of the waste. .. throughput and high cost Wheeled cart and charging door are mechanical complexities Limited application to contaminated large metal parts Flexible temperature programs for destruction requirements References Acharya, P., S.G DeCicco, and R.G Novak, 1991, Factors that can influence and control the emissions of dioxins and furans from hazardous waste incinerators, 84th Annual Meeting of the Air and Waste. .. important Off-Gas System The function of the off-gas system is to render the gaseous and particulate emissions from the melter suitable for safe and compliant discharge to the atmosphere Vitrification off-gas systems vary considerably in complexity, depending on the application and the amounts and types of hazardous constituents present in the waste However, they are typically composed of a train of standard . liquid waste incineration) 5. Ash removal system to remove ash and non-combustibles from the primary chamber, and cool it for subsequent handling and treatment 6. Ash and non-combustibles treatment. to the treatment of radioactive and mixed wastes. Radioactive waste incineration has been practiced since the 1950s for volume reduction and con- version of slightly contaminated fibrous waste. industrial wastes, municipal wastes, environmental restoration clean-ups, radioactive wastes, medical wastes, and virtually any organic material that represents an environmental hazard. This chapter